Fluid pump or motor of the rotary screw type



G. RATHMAN April 12, 1955 FLUID PUMP OR MOTOR OF THE ROTARY SCREW TYPEFiled April 6. 1953 5 Sheets-Sheet 1 INVENTOR ATTORNEXQSY G. RATHMANFLUID PUMP OR MOTOR OF THE ROTARY SCREW TYPE Filed April 6. 1953 5Sheets-Sheet 2 1N VENTOR G Lbr Rathman BY @mm1/,MPM

ATTORNEKS April 12, 1955 G. RATHMAN 2,705,922

FLUID PUMP OR MOTOR OF' THE ROTARY SCREW TYPE asv/. l .26

coMPREssoN RATIO- coMPREssloN RATIO coMPREssloN RATIO INVENTOR Gil/bertRai/unan Carnahan/7mm sv/Zan ATTORNEYS G. RATHMAN April 12, 1955 FLUIDPUMP OR MOTOR OF THE ROTARY SCREW TYPE Filed April 6, 1953 5Sheets-Sheet 4 1N VENTOR ATTORNEYS' G. RATHMAN April 12, 1955 FLUID PUMPOR MOTOR OF THE ROTARY SCREW TYPE Filed April e, 1953 5 shets-sheet 5INVENTOR G Lber Ralunan/ BY @WWW/,Mm Wm ATTORN E YLS United StatesAPatent O FLUID PUMP GR MOTR F THE ROTARY SCREW TYPE Gilbert Rathman,Union, N. J., assigner to Dresser Industries, Inc., Bradford, Pa., acorporation of Pennsyl vanta Application April 6, 1953, Serial No.346,844

16 Ciams. (Cl. 10S-12S) This invention relates to rotary screw pumps andmotors of the positive displacement type comprising intermeshing,helically ribbed rotors which are adapted either for transporting orcompresing uids, or for operation as ex pansible fluid engines, and isparticularly directed to apparatus of this character wherein each rotorrib or thread is half male and half female, i. e., convex on one sideand concave on the other side. For examples of the forms ot rotors towhich the invention pertains, reference may be had to Nuebling PatentNo. 1,233,599, dated July 17, and my own Patent No. 2,511,878, datedlune 20,

Although the devices of the present invention are reversible inoperation so as to function with equally high efficiency as either pumpsor motors, the following descn'ption will, in the interest ofsimplicity, designate said devices as pumps or blowers and usephraseolog generally applicable to air blowers and compressors. By sodoing, however, it is not intended to limit the scope of the inventionto pumps, blowers and compressors, even though it is in this field thatthe inventive concept would appear to iind its greatest utility at thepresent time.

The pump disclosed in my above idenied patent, upon which the presentinvention is an improvement, is characterized by the combination of apair of coacting rotors, each having a single helical rib or threadconvex on one side and concave on the other, which rotate in intermeshedrelation with a one-to-one gear ratio in a casing continuously open atthe inlet end to a source of low pressure iiuid and having intermittentconnection at the other end with a discharge conduit wherein an equal orhigher pressure prevails. Communication between the discharge conduitand the fluid transporting and compressing spaces defined by the rotorribs is controlled in such a manner that the iiuid is confined in saidspaces until the desired pressure is built up, whereupon, once in everyrevolution of the rotors, each space is opened to the discharge conduitthrough a passageway or port which faces, and lies within the axiallyprojected cross section of, the threaded portion of that rotor which hasthe concave side of its thread facing the discharge end of the pump. Thelatter rotor may conveniently be called the discharge or driving rotor,while the other is known as the mating or driven rotor.

In this earlier type of pump, the discharge of fluid from the rotors isin an axial direction and is controlled by a discharge port in the endwall of the casing of predetermined coniiguration and volumetriccapacity which is opened and closed periodically by rotation of thedischarge rotor itself, the end of the rotor rib or thread serving tocover and uncover the port as the rotor turns. With this construction,it is possible to maintain a constant iiow ot gas or other fluid intothe discharge line at a predetermined pressure without objectionablesurging or other variable pressure conditions in the fluid at thedischarge end of the pump, and to obtain an adiabatic internalcompression up to at least a 3:1 ratio, or a discharge pressure of 30pounds per square inch or more (gauge).

One of the objects of the present invention is to provide an improvedform of screw type pump or motor embodying half male, half female rotorthreads which, for compression or expansion ratios of about 2:1 or less,is of smaller size, less weight and lower cost, and is capable of higherrotational speeds, than the construction represented by the abovementioned Patent No. 2,511,878.

Another object is to provide a blower or compressor of the characterdescribed with radially disposed intake and 8 0 Patented Apr. 12, 1955discharge ports of novel construction which are especially designed withreference to the form of the rotors to provide the compression ratiodesired.

A further object is to provide a pump of the rotary screw type having abuilt-in compression ratio of not more than about 2:1 embodying improvedmeans for discharging the compressed liuid and preventing the entrapmentthereof between the rotors and the discharge end of the casing.

These and other objects, including provision of a device of thecharacter described which is reversible in operation with no loss ineflciency, will appear more fully upon consideration of the detaileddescription of certain embodiments of the invention which follows.Although several specifically diiferent structures are described andillustrated in the accompanying drawings, it is to be expresslyunderstood that these drawings are exemplary only and are not to beconstrued as dening the limits of the invention, for which latterpurpose reference should be had to the appended claims.

Referring now to the drawings, wherein like reference charactersindicate like parts throughout the several views and all of the Viewsare at least partially diagrammatic:

Fig. l is a side view of one form of screw pump or compressor embodyingthe invention with the inlet side of the casing removed and withportions of the rotors shown in vertically axial section;

Figs. 2 and 3 are plan and end elevation views, respectively, of thedevice shown in Fig. 1;

Fig. 4 is an irregular transverse sectional View of the construction ofFigs. l-3 taken approximately on the line 4 4 in Fig. 2;

Fig. 5 is a side view of the pump of Figs. 1-4 taken from the dischargeside with the portion of the casing which defines the discharge portbroken away so as to show the configuration of said port in relation tothe rotor threads;

Figs. 6a, 6b and 6c are diagrams indicating how the size of thedischarge port may be varied in order to vary the compression ratio;

Fig. 7 is a plan View of the device of Figs. 1 6 with the casing shownin section, the section being taken substantially on the line 7 7 inFig. 1;

Fig. 8 is a sectional view of the structure of Fig. 7 takensubstantially on the line 8 3 in the latter gure;

Fig. 9 is a fragmentary view similar to Fig. 7 of the discharge end ofanother embodiment of the invention, the sectioning of the casing inthis view being irregular in order to better illustrate the constructioninvolved;

Fig. l0 is a sectional view of the structure of Fig. 9 talensubstantially on the line 10-10 in the latter iigure; an

Figs. 1l and 12 are views similar to Figs. 9 and 10, respectively, of athird construction embodying the invention.

Referring now to Figs. 1-5, 7 and 8, the pump structure shown thereincomprises a casing made up of two complementary side sections 21 and 22and a pair of end sections or heads 23 and 24 provided with supportingbases 25 and 26, respectively, the two side sections being removablysecured to one another along a vertical plane passing through the axesof the pump rotors in any suitable manner, as by anges and bolts (notshown), while the end sections 23 and 24 are similarly connected to theanged ends of the side sections. As shown best in Figs. 3 and 4, themain body of the casing formed by the two side sections is substantially3-shaped in cross section, consisting of a pair of hollow cylinders inpartially overlapped relation with their axes parallel and verticallyottset from one another. Side section 21 carries adjacent one endthereof a laterally projecting fluid intake conduit 27, while sidesection 22 is provided with a similar fluid discharge conduit 28adjacent the other end of the casing.

Housed in each of casing heads 23 and 24 are a pair of combinationradial and end thrust bearings 29 which rotatably support the shafts 30and 3l of a pair of intermeshed, helically threaded rotors 32 and 33adapted, in known manner, to transport air, gas or other iluid from theintake conduit 27, through the casing and out through the dischargeconduit 28, and at the same time to compress the uid prior to discharge.The shaft 30 of rotor 32, hereinafter referred to as the driving ordischarge rotor, projects outwardly of casing head 23 at the intake endof the casing, and is adapted to be connected to a suitable source ofpower for turning the driving rotor in the direction indicated by thearrows in the iigures. The shaft 31 of the second rotor 33, hereinafterreferred to as the driven or mating rotor, is drivably connected toshaft 30 of the driving rotor by means of gears 34 housed in casing head23 which are adapted to rotate both rotors at the same speed.

'Ihe rotors 32 and 33 are keyed to their respective shafts 30 and 31 forrotation therewith, and are held against axial movement along saidshafts, to the right as viewed in Fig. 1, by stop shoulders 35 and 36formed on the shafts. The driving rotor 32 is provided with a singlehelical thread or rib 37 having at least one full turn or convolution,the outer peripheral surface of which has a running fit in the upperportion of the casing formed by side sections 21 and 22. The drivenrotor 33 is similarly provided with a thread or rib 38 of the samelength as the thread 37 and having a running t in the lower portion ofthe casing.

As best illustrated in Fig. l, each of the threads or ribs 37 and 38 isconcave in longitudinal cross section at one side, while the oppositeside is convex; i. e., each thread is half male and half female. Forexample, the left side 39 of the driving thread 37 is concave, as viewedin Fig. l, while the right side 40 is convex, or substantially so. Thedriven thread 38 is oppositely formed in that its left side 41 isconvex, or practically convex, while the right side 42 is concave. Theresult is that the two rotors are so formed that the similarly shapedsides of the threads face one another, and that the concave side 39 ofdriving thread 37 of the discharge rotor faces the end wall formed bycasing head 24 at the discharge end of the casing. It will also be notedthat, in this form of rotor construction, which is the subject matter ofmy previously mentioned Patent No. 2,511,878, thread 37 of the dischargerotor is relatively thin in an axial direction in comparison with thread38 of the driven rotor, and that the groove 43 between the turns ofthread 37 is correspondingly wider than the groove 44 of the drivenrotor.

By reference to Fig. 4, it will be seen that each rotor exhibits in anysection perpendicular to its axis a compound curved outline consistingof an outer peripheral surface 45 of cylindrical curvature conforming tothe curvature of the inside wall of the casing in which it rotates, aninner root or dedendum circle 46 concentric with the associated rotorshaft, a concave side 47 connecting one end of the outer peripheralsurface 45 with oneend of the exposed portion of the root circle 46, anda curvex side 48 connecting the other end of the peripheral surface withthe root circle. The concave side 47 of the thread is of epicycloidalshape, while the convex side 48 has a curvature substantially that of anArchimedean spiral.

The stop shoulders 3S and 36 on the rotor shafts are located, as shownin Figs. l and 7, a substantial distance inwardly from the wall ofcasing head 23 which closes the intake end of the casing so as toprovide a relatively large uid intake chamber 49 which is in permanentlyopen, direct communication with the uid intake conduit 27 and alsocommunicates with the intake ends of the fluid transporting andcompressing spaces 50 dened by the rotor threads 37 and 38 and thesurrounding wall of the casing. In accordance with the presentinvention, communication between intake conduit 27 and intake chamber4-9 is provided by an intake port 51 which is formed by a radiallyoutwardly dished or odset portion of the Wall of side section 21 of thecasing and is of substantially greater area than intake conduit 27. Asindicated by the broken lines in Fig. l, intake port 51 has an areaalmost half that of casing side section 21 and is of irregular shapeconforming in part to the peripheral edges of the rotor threads.

In the form shown, port 51 has an end edge a parallel to and located insubstantially the same plane with thc inner face of the wall formed bycasing head 23, a pair of parallel side edges b and c substantiallycoincident withthe upper and lower edges of side section 2l, and anotherend edge of irregular form dened by two lines d and e parallel to theperipheral edges of rotor threads 37 and 38, respectively, whichconverge toward the opposite casing head 24 but do not intersect, and athird line f parallel to the rotor axes connecting the other two lines,said third line f lying closer to the axis of driven rotor 33 than tothe axis of driving rotor 32. If desired, the two side edges b and c ofthe intake port may be brought closer together than in the embodimentillustrated, although their spacing should be maintained at least asgreat as the distance between the rotor axes. The axial dimensions ofport 51 may also be varied as described, as long as they are notincreased to the point where there is direct communication through thefluid transporting and compressing spaces 50 between intake port 51 andthe discharge port 52 next to be described.

As in the case of the intake port, discharge port 52 is formed by aradially outwardly dished portion of casing side section 22 and is of ashape directly related to and dependent upon the form of the rotorthreads. The size or area of port 52 establishes the compression ratioof the device. In the structure shown in Figs. l-5, the discharge porthas been given its maximum permissible size corresponding to a 1:1compression ratio, i. e., the case in which the pump acts solely as auid transport mechanism without internal compression.

As shown best in Fig. 5, port 52 has one edge g parallel to andsubstantially coplanar with the wall formed by casing head 24 at thedischarge end of the casing against which the discharge ends of rotorthreads 37 and 38 abut, the remaining edges being delined by twononintersecting lines h and i parallel to the peripheral edges of therotor threads, line h intersecting edge g closely adjacent the loweredge of casing section 22, a third line j parallel to the rotor axesconnecting the adjacent ends of lines h and i and having a length lessthan the axial dimension of the outer peripheral surface of thread 37 ofthe driving rotor and lying closer to the axis of said rotor than to theaxis of driven rotor 33, and a fourth line k substantially coincidentwith the upper edge of zasing section 22 joining edge g and the upperend of ine z.

In order to determine the locations of lines h, i and j, the rotors areturned to the position wherein the portion of fluid transporting andcompressing space 50 adjacent casing head 24 at the discharge end of thedevice has just been cut of from communication with intake port 51; i.e., when the rotors reach the position where they are about to begincompression of the fluid contained in that portion of space 50 which isconfined between the end wall formed by casing head 24 and the last halfconvolutions of the rotor threads adjacent said wall. At this time, theend of the leading edge of driving rotor thread 37 lies in the plane ofthe rotor axes adjacent the side wall of the casing at the top thereof,while the end of the trailing edge of driven rotor thread 3S lies in thesame plane adjacent the casing side wall at the bottom thereof. With therotors in this position, i. e., the position shown in Fig. 5, themaximum permissible size of discharge port 52 is defined by the tracesupon the inner surface of casing side section 22 of the trailingperipheral edges l and m of the last half convolutions of the rotorthreads adjacent the casing head 24 and a line joining said tracesparallel to the rotor axes lying closer to the axis of driving rotor 32than to the axis of driven rotor 33. While this method will provide thetheoretically correct, maximum permissible size of discharge port, it ispreferable, in order to insure adequate sealing between the intake anddischarge ports, to make the discharge port smaller than thetheoretically correct maximum, as has been done in Fig. 5, by locatingthe edges h and 1' of the port slightly closer to casing head 24 thanthe traces of trailing edges l and m of threads 37 and 38, respectively.

In order to establish the shape and size of discharge port 52 for anycompression ratio between 1:1 and 2:1, it is only necessary to place therotors in the position wherein the uid pocketed between the rotorthreads and the end wall 24 has been compressed to the desired pressureand then trace the trailing edges of the discharge ends of the rotorthreads in the manner above described, again preferably reducing thesize of the port slightly below the theoretically correct size to insureproper sealing. See, for example, the diagrams of Figs. 6a, 6b and 6cwherein have been indicated the relative shapes and sizes of dischargeport for compression ratios of 1:1, 8:5 and 2:1, respectively. ln eachinstance, it will be noted that the major portion of the area of thedischarge port lies radially opposite the unmeshed portion of thread 37of the driving rotor 32.

said rst port, a second port formed entirely in the side wall of saidcasing adjacent the other end thereof and providing communicationbetween the iiuid receiving space and said second conduit, and a secondwall perpen dicular to the axes of said rotors closing the end of said`casing adjacent said second port and facing the concave and convexsides of the threads of the first and second rotors, respectively, saidsecond port having one edge parallel to and in substantially the sameplane as said second wall and another edge of irregular form defined bytwo non-intersecting lines parallel to the peripheral edges of therespective rotor threads and converging toward said first Wall and athird line parallel to the rotor axes connecting the other two lines,said third line having a length less than the axial dimension of theouter peripheral surface of the thread of the first rotor and lyingcloser to the axis of said first rotor than to the axis of the secondrotor.

2. A rotary screw type fluid pump or motor as defined in claim l whereinthe maximum size of said second port is defined by the trailing edges ofthe last half convolutions of the rotor threads adjacent the second wallwhen the rotors are so positioned that the end of the leading edge ofthe thread of the first rotor lies in the same plane as the rotor axesand adjacent the side wall of the casmg.

3. A rotary screw type iiuid pump or motor as defined in claim 1including a passageway in the second wall leading from a point oppositethe unmeshed portion of the thread of the first rotor, adjacent the hubof said rotor and the periphery of the thread of the second rotor, tothe second conduit, said passageway being adapted to pass fiuid betweenthe fluid receiving space and said second conduit independently of thesecond port.

4. A rotary screw type uid pump or motor as defined in claim 3 whereinsaid passageway consists of a curved groove in said second wallparalleling the periphery of the thread of the second rotor andextending from a point opposite the hub of said first rotor to a pointopposite the periphery of the thread thereof.

5. A rotary screw type fluid pump or motor as defined in claim 3 whereineach rotor thread exhibits in any section perpendicular to its axis acompound curved outline defined by a portion of the root circle of saidthread, a port-ion of the cylindrical periphery thereof and two curves,one concave and the other convex, connecting said portions of the rootcircle and cylindrical periphery, and wherein said passagewav consistsof a recess in said second wall having an outline defined by two linessubstantially coincident with portions of the root circle andcylindrical periphery of the thread of said first rotor, a third linesubstantially coincident with the convex curve of the outline of thethread of said first rotor, and a fourth line substantially coincidentwith a portion of the cylindrical periphery of the thread of said secondrotor, the side of said recess defined by the line substantiallycoincident with a portion of the cylindrical periphery of said rst rotorbeing open to sa-id second conduit.

6. A rotary screw type fluid pump or motor as defined in claim l whereinsaid first port has one end edge parallel to and adjacent the plane ofsaid first wall, a pair of side edges parallel to and spaced apartfurther than the axes of said rotors, and another end edge of irregularform defined by two non-intersecting lines parallel to the peripheraledges of said rotor threads and converging toward said second wall and athird line parallel to the rotor axes connecting the other two lines,said third line lying closer to the axis of said second rotor than tothe axis of said first rotor.

7. A rotary screw type fluid pump comprising a pair of intermeshinghelically threaded rotors interconnected to drive one rotor from theother at a one-to-one ratio, each of said rotors having a thread whichis convex on one side and concave on the opposite side and has an outerperipheral surface of helically cylindrical form. said rotors being sointermeshed that the concave and convex sides of the thread on the firstrotor face the concave and convex sides, respectively, of the thread onthe second rotor, a casing for said rotors having a side wallcooperating with the rotor threads to form a fiuid pumping space and endwalls preventing the ingress and egress of fluid in an axial direction,fiuid inlet and outlet conduits connected to said casing, a iiuid inletport formed entirely in the side wall of said casing adjacent one endthereof providing communication between the inlet conduit and the iiuidpumping space defined by the rotor threads and the casing, and a iiuidoutlet port formed entirely in the side Wall of said casing on the sideopposite the inlet port adjacent the other end of said casing andproviding communication between said fiuid pumping space and the outletconduit, the shape and size of said outlet port for any given outletpressure of the iiuid being defined substantially by the end wall of thecasing at the outlet end thereof and the traces upon the side wall ofthe trailing peripheral edges of the last half convolutions of the rotorthreads adjacent said end wall.

8. A rotary screw type fiuid pump as defined in claim 7 wherein themaximum size of said outlet port is defined by the traces upon the sidewall of the trailing peripheral edges of the last half convolutions ofthe rotor threads adjacent the end wall of the casing at the outlet endthereof when the rotors are so positioned that the end of the leadingedge of the thread of the first rotor lies in the same plane as therotor axes and adjacent the side wall of the casing.

9. A rotary screw type iiuid pump as defined in claim 7 including arelief passageway in the end wall of the casing at the outlet endthereof for venting the fluid pocketed in the fluid pumping spacebetween said end wall and the end of the thread of said first rotorduring the partial rotation of said rotors immediately following closureof communication between said pumping space and the outlet port.

l0. A rotary screw type iiuid pump as defined in claim 9 wherein therelief passageway leads from a point opposite the unmeshed portion ofthe thread of the first rotor, adjacent the hub of said rotor and theperiphery of the thread of the second rotor, to the outlet conduit, saidpassageway being adapted to pass fluid from the iiuid pumping space tosaid outlet conduit independently of the outlet port.

ll. A rotary screw type iiuid pump as dened in claim 9 wherein saidrelief passageway consists of a curved groove in the end wall of thecasing at the outlet end thereof paralleling the periphery of the threadof the second rotor and extending from a point opposite the hub of saidfirst rotor to a point opposite the periphery of the thread thereof.

l2. A rotary screw type uid pump as defined in claim 9 wherein eachrotor thread exhibits in any section perpendicular to its axis acompound curved outline defined by a portion of the root circle of saidthread, a portion of the cylindrical periphery thereof and two curves,one concave and the other convex, connecting said portions of the rootcircle and cylindrical periphery, and wherein said relief passagewayconsists of a recess in the end wall of the casing at the outlet endthereof having an outline defined by two lines substantially coincidentwith portions of the root circle and cylindrical periphery of the threadof said first rotor, a third line substantially coincident with theconvex curve of the outline of the thread of said first rotor, and afourth line substantially coincident with a portion of the cylindricalperiphery of the thread of said second rotor, the side of said recessdefined by the line substantially coincident with a portion of thecylindrical periphery of said rst rotor being open to said outletconduit.

13. A rotary screw type fluid pump comprising a pair of intermeshinghelically threaded rotors interconnected to drive one rotor from theother at a one-to-one ratio, each of said rotors having a thread whichis convex on one side and concave on the opposite side and has an outerperipheral surface of helically cylindrical form, said rotors being sointermeshed that the concave and convex sides of the thread on the firstrotor face the concave and convex sides, respectively, of the thread onthe second rotor, a casing for said rotors having first and second sidewall sections adapted to be connected together in the plane of the rotoraxes and cooperating with the rotor threads to form a fluid pumpingspace and end walls preventing the ingress and egress of fiuid in anaxial direction, an inlet conduit connected to said first side wallsection, an outlet conduit connected to said second side wall section, afluid inlet port formed entirely in said first side wall sectionadjacent one end thereof providing communication between said fluidinlet conduit and the fiuid pumping space defined by the rotor threadsand the casing, and a fiuid outlet port formed entirely in said secondside wall section adjacent the other end of said casing and providingcommunication between said uid pumping space and said outlet conduit,each of said inlet and output ports having a shape dened in part by thetraces upon the associated side wall section of the peripheral edges ofsaid rotor threads.

14. A rotary screw type uid pump as defined in claim 13 wherein each ofsaid inlet and outlet ports has one edge parallel to and insubstantially the same plane as the adjacent end wall of the casing.

15. In a rotary screw type iluid pump of the type comprising a pair ofintermeshed helically threaded rotors interconnected to drive one rotorfrom the other at a one-to-one ratio, each of said rotors having athread which is convex on one side and concave on the opposite side andhas an outer peripheral surface of helically cylindrical form, and acasing for said rotors having a side wall cooperating with the rotorthreads to form a uid pumping space and end walls preventing the ingressand egress of uid in an axial direction, a fluid inlet conduit and afluid outlet conduit connected to said casing and extending in a radialdirection with respect to said rotors, and a uid outlet port formedentirely in said side wall adjacent one end of said casing providingdirect communication between said outlet conduit and the uid ReferencesCited in the file of this patent UNITED STATES PATENTS 2,111,568 Lysholmet al Mar. 22, 1938 2,174,522 Lysholm Oct. 3, 1939 2,266,820 Smith Dec.23, 1941 2,287,716 Whitfield June 23, 1942 2,474,653 Boestad June 28,1949 2,481,527 Nilsson Sept. 13, 1949 2,511,878 Rathman June 20, 19502,578,196 Montelius Dec. 11, 1951 2,620,968 Nilsson Dec. 9, 1952 FOREIGNPATENTS 124,376 Sweden Ian. 20, 1949

